1. Field of the Invention
The present invention relates to a semiconductor device including an oxide semiconductor, a display device including the semiconductor device, and a manufacturing method thereof.
2. Description of the Related Art
There are a wide variety of metal oxides and such metal oxides are used for various applications. Indium oxide is a well-known material and is used as a light-transmitting electrode material which is necessary for liquid crystal displays and the like.
Some metal oxides have semiconductor characteristics. As metal oxides having semiconductor characteristics, for example, there are tungsten oxide, tin oxide, indium oxide, zinc oxide, and the like, and a transistor having such a metal oxide having semiconductor characteristics in its channel formation region has been proposed (Patent Documents 1 to 4, Non-Patent Document 1).
As metal oxides, multi-component oxides as well as single-component oxides are known. For example, a homologous compound, InGaO3(ZnO)m (m is natural number) is known as a multi-component oxide having In, Ga and Zn (Non-Patent Documents 2 to 4).
Further, it is confirmed that such an oxide semiconductor made of In—Ga—Zn-based oxide is applicable to a channel layer of a transistor (Patent Document 5 and Non-Patent Documents 5 and 6).
Having features such as high mobility, a light-transmitting property, and capability of being formed at low temperature, an In—Ga—Zn-based oxide has been attracting attention as a material for a pixel transistor of a next-generation display typified by a flexible display.
However, In and Ga in the In—Ga—Zn-based oxide are rare metals and very expensive, which may lead to an increase in transistor cost. Furthermore, In and Ga resources are in danger of depletion, and from an environment standpoint, discovery of an alternative material is desired.